A paint program with PCHG modes would be cool, but I guess it would be a lot of work to do it.

So instead, a cli program which could count the number of each line and then indicate those with more that 15 colors (the max allowed by HamLab) so that one could draw in 256 colors (out of 4096) with a paint program like Brilliance and then verify, thanks to this kind of scanline colour counting program, which scanline exceed the number of colour displayable by the PCHG format. It would help a lot !